1. Field of the Invention
The present invention relates to a polarizer, and more particularly, to a polarizer used in a liquid crystal display. Although the polarizer of the present invention is applicable to a wide range of applications, it is especially applicable to a touch panel and a flat panel display integrated with the touch panel.
2. Discussion of the Related Art
Generally, a “polarizer” is attached to each surface of a liquid crystal display (LCD) of a flat panel display device for linear polarization of a visible light ray. A “touch panel” is an input device used, instead of a keyboard or a mouse. Such applications for the touch panel include a CAD, a production system, a game machine, a KIOSK, a POS and medical applications. The touch panel is mounted to a display screen which is an output device so that a user can make various input operations for controlling the device by manually pressing a desired position in the screen while viewing the display screen.
A touch panel is classified into a resistive film system or a capacitance system depending on its operational principle. The touch panel of a resistive film system operates by sensing a voltage or current change at a contact point of two opposite conductive layers (or resistive films) that is pressed by a user and then converting it into a coordinate value when a voltage has been applied to the two opposite conductive layers.
On the other hand, in the touch panel of a capacitance system, a small amount of electric charges is accumulated in a single transparent conductive film or transparent conductive glass in accordance with a capacitance coupling between a stylus (a pen-type input device) and the transparent conductive film at a contact point pressed by a user when alternating charge and discharge states of the capacitance are being repeated. The capacitance system touch panel operates by reading the amount of electric charges from four input points and then converting it into a coordinate value. In such capacitance system touch panel, an electrical power is applied to the stylus.
The conventional flat panel display employing a touch panel of resistive film system will be described below.
FIG. 1 is a sectional view showing the structure of a conventional flat panel display of an additive type touch panel. In FIG. 1, touch panel 50 is added to an upper surface of flat panel display 40 including lower polarizer 10, LCD 20 and upper polarizer 30. In such a conventional additive type touch panel flat panel display, since touch panel 50 is located at the uppermost portion of the flat panel display and externally exposed, it is referred to as an “outer touch panel”.
In the additive type touch panel flat panel display, as shown in FIG. 1, lower polarizer 10 is provided with optical film 12 for polarizing light at the center thereof, upper film 13 and lower film 11. The upper and lower films mechanically support optical film 12 at the upper and lower surfaces, respectively. LCD 20 includes lower glass 21 and upper glass 22 that surround a liquid crystal layer. The liquid crystal layer is provided between lower glass 22 and upper glass 22. Upper polarizer 30 includes lower film 31, optical film 32, and upper film 33 in a similar manner to lower polarizer 10.
Touch panel 50 is provided with lower sheet 51 including a transparent film at the lower portion thereof to serve as a resistive film, upper sheet 52 including a transparent film at the upper portion thereof to serve as a resistive film, bus bar 53 serving as an electrode for applying a voltage to two resistive films between the lower sheet and upper sheet 52, tail 54 for connecting bus bar 53 to a controller over flat panel display 40, and a plurality of dot spacers 55 positioned on lower sheet 51 to space upper sheet 52 from the lower sheet 51. Lower sheet 51 includes a base film or glass layer and a conductive layer (or resistive film layer). Upper sheet 52 includes a conductive layer (or resistive film layer), a transparent conductive film layer and an anti-dazzling hard-coating layer. Adhesive 60 may be replaced by a double-face adhesive tape.
The conventional additive type touch panel flat panel display as described above has a problem in that, since touch panel 50 including lower sheet 51 and upper sheet 52 is added to the upper portion of flat panel display 40 which increases the entire bulk and weight, it is difficult to apply the touch panel to an LCD monitor, a notebook or personal computer, etc., which require light weight and thin characteristics. Also, the conventional additive type touch panel flat panel display has a problem in that, there is a large difference of refraction index with five boundary surfaces and a relatively large reflection as indicated by dotted lines in FIG. 1. Such problem results in poor light transmissivity.
FIG. 2 is a sectional view showing the structure of a conventional integral type touch panel flat panel display. Referring to FIG. 2, the conventional integral type touch panel flat panel display includes lower polarizer 10, LCD 20, touch panel 50 and upper polarizer 30 that are sequentially disposed. Touch panel 50 is inserted into flat panel display 40 including lower polarizer 10, LCD 20 and upper polarizer 30 to thereby form an integral type. In such a conventional flat panel display, since touch panel 50 is located at an inner side of the upper polarizer 30, it is referred to as an “inner touch panel”.
Such a conventional integral type touch panel flat panel display has a structure almost analogous to the additive type touch panel flat panel display, except that touch panel 50 in the integral type is located between upper polarizer 30 and LCD 20 while touch panel 50 in the additive type is located over upper polarizer 30. The light transmissivity in the integral type is somewhat improved over the additive type.
The conventional integral type as described above also has a problem in that, since touch panel 50 including lower sheet 51 and upper sheet 52 is used similarly to the conventional additive type which increases the entire bulk and weight, it is difficult to apply the touch panel to an LCD monitor, a notebook or a personal computer, etc., which require light weight and thin characteristics. Also, the conventional additive type touch panel flat panel display has a problem in that, there is a large difference in the refraction index with five boundary surfaces and a relatively large reflection as indicated by dotted lines in FIG. 2. Such problem results in poor light transmissivity.
Furthermore, the conventional integral type touch panel flat panel display is limited in that, a light-isotropic film must be used for transparent conductive films of upper sheet 52 and lower sheet 51 of touch panel 50 because touch panel 50 is inserted between lower polarizer 10 and the upper polarizer. According to a disclosure in the Japanese Patent Laid-open No. 9-24571, if a light-isotropic film is not used for the transparent conductive films of upper sheet 52 and lower sheet 51 of touch panel 50 that is inserted between lower polarizer 10 and upper polarizer 30, then an optical axis is not matched causing a coloration or a light interference due to an interference with lower polarizer 10.
Yet another problem with the conventional touch panel integral type flat panel display is that because touch panel 50 is inserted between upper polarizer 30 and LCD 20, mechanical characteristics such as a degree of hardness, heat-proof and scratch-proof, etc. related to upper sheet 52 of touch panel 50 must be provided to upper polarizer 30.